frostbite can happen very quickly. how quickly depends on a number of factors - what you are wearing, how many calories you consumed, alcohol/tobacco use, temperature, wind speed, among other things. the National Weather Service estimates that in severe cold and wind conditions, frostbite can occur in as little as five minutes. (-20F temperature plus 35 mph winds, for example).

because cell/smart phones require either bare skin for a touch screen or very thin glove liners to tap a keyboard, this presents people with the monumentally stupid opportunity to get frostbite for no good reason. my hands are staying in the glove liners and in the mitts on a winter summit unless it's a lot more important than a phone call or a text message. i wouldn't try to use my phone from the top of Mt. Washington or Mt. Marcy in the winter, let alone Everest, unless i were in serious distress.